Where copyright exists on content data such as music data or image data, unless suitable measures for copyright protection are taken, there is a fear that the right of the author is infringed. On the other hand, when first priority is given to the copyright protection and the circulation of the content data is impeded, this becomes contrarily disadvantageous also to the copyright holder who can collect the copyright fee when the copyrighted work is copied.
The distribution of content data as an object of copyright protection is performed mainly through a digital communication network, broadcasting waves or the like. When a user uses such data, the data is usually recorded once on some storage medium and then is played back by a playback device. At present, as a storage device which has large capacity, has high access performance, and has a control function, a magnetic disk device is known. Almost all the magnetic disk devices are fixedly incorporated in recorder/players, and there is no such a magnetic disk device that data recorded thereon can be used by another playback device. However, from the viewpoint of convenience, there is a possibility that the use of a portable storage device grows in future. On the other hand, although the capacity is small as compared with the magnetic disk device, a memory card is known as a portable storage device with a copyright protection function.
As a device to reproduce data, a recorder/player used to receive the delivery of such data, or a portable dedicated playback device is used. In a recorder/player to which a portable storage device can be connected, in order to protect the copyright of data recorded on the storage device, it is important to take security measures for the recorder/player and the storage device, so that the data recorded on the storage device can not be reproduced beyond the scope of conditions insisted by the copyright holder. When the security measures are taken for the equipment, with respect to data exchange performed in an area which can be freely accessed from the inside and outside of the device, it is necessary that an authentication process is performed between the devices in which the data exchange is performed, or an encryption process is performed on the data itself, so that an access to the data is not freely performed in clear text. On the other hand, as the authentication process or the encryption process as stated above becomes strict, many processes are required from the time when the user issues a data use request to the time when the data can be actually used, and resultantly, there is a possibility that a situation occurs in which the reproduction of the data can not be smoothly performed.
For example, Patent Publication No. WO01/013358 and Patent Publication No. WO01/043339 propose that digital data to be used is encrypted, and a key for decrypting it and a use condition at the decryption can not be illegally acquired or falsified, so that the copyright is protected. Japanese Patent Publication No. 2004-302701 discloses a technique relating to a storage device which divides plural encryption input/output processes sent from a host device into plural procedures and processes them in parallel in order to improve tamper resistant features when the data to be concealed is encrypted and is inputted/outputted between the storage device and the host device.
Each of the above patent documents discloses the process in which digital data is encrypted, and the key for decrypting it and the use condition are transferred between the two equipments. However, there is a demand that even if the content is encrypted, the transfer or copy from an equipment in which it is recorded to another equipment without limitation should not be performed.